A wide variety of automated chemical analyzers are used to analyze patient specimens. These clinical analyzers may conduct assays using reagents to identify one or more analytes in, or characteristics of, a biological liquid such as urine, blood serum or plasma, cerebrospinal liquids, and the like. For convenience and safety reasons, these biological liquids may be contained within sample containers (e.g., sample tubes) that are generally capped.
Improvements in clinical analyzer technology have been accompanied by advances in pre-analytical sample preparation and handling operations such as sample sorting, sample container centrifugation, cap removal, and the like by automated pre-analytical sample preparation systems called Laboratory Automation Systems (LASs). LASs automatically transport biological liquid samples in sample containers to a number of sample processing stations that have been linked together. These LASs may handle a number of different patient specimens contained in standard, barcode-labeled, and evacuated sample containers. The barcode label may contain an accession number that may be correlated to demographic information that may be entered into a hospital's Laboratory Information System (LIS) along with test orders and other desired information. An operator may place the labeled sample containers (e.g., sample tubes) onto the LAS system, which may automatically route the sample containers for pre-analytical operations such as centrifugation, decapping, and aliquot preparation, prior to the specimen being subjected to clinical analysis by one or more analytical stations that may also be linked to, or part of, the LAS.
For certain clinical assays, a serum or plasma portion (obtained from whole blood by centrifugation) may be used. To prevent clotting, an anticoagulant such as citrate or heparin may be added to the blood specimen. After centrifuging and subsequent de-capping, the open sample container (e.g., tube) may be transported to an appropriate clinical analyzer that may extract liquid specimen from the sample container and combine the specimen with one or more reagents in reaction containers (e.g., cuvettes or cups). Analytical measurements may then be performed, using, for example, photometric or fluorometric absorption readings or the like. The measurements allow determination of values from which an amount of analyte related to the health of the patient may be determined using well-known techniques. Unfortunately, the presence of certain components (e.g., interferents) such as hemolysis (ruptured red blood cells), icterus (excessive bilirubin), and lipemia (high, visible lipid content) (hereinafter “HIL”) in the specimen as a result of some preexisting sample condition or processing may adversely affect an accuracy of the analyte measurement obtained from the clinical analyzer.
In some cases, the integrity of the serum or plasma portion of the specimen may affect the interpretation of the results, i.e., the analyte reading of the clinical analyzer. For example, pre-analytical variables in the serum or plasma portion, which are not related to the patient disease state, may cause a different interpretation of the disease condition of the patient. Pre-analytical variables include HIL. Typically, the integrity of the serum or plasma portion of the specimen is visually inspected by a skilled laboratory technician. This may involve a review of the color of the serum or plasma portion of the specimen. A normal serum or plasma portion has a light yellow to light amber color.
A serum or plasma portion containing hemolysis may be quite reddish in color. Interferents may arise, for example, if an excess number of red blood cells are damaged, possibly during venipuncture, centrifugation, or prolonged storage. When red blood cells are injured, they release low density, reddish-colored hemoglobin into the specimen causing a reddish-colored sample that is said to exhibit “hemolysis.” The presence of free hemoglobin may be used to measure the degree of hemolysis and, when the hemoglobin concentration exceeds about 20 mg/dl, the hemoglobin may interfere with the colorimetric determination of analytes in the clinical analyzer due to the reddish interferent contained in the specimen.
A sample containing icterus may be dark yellow/brown in color. Such interferents may arise, for example, from an excess of bilirubin, the result of decaying red blood cells being converted in the spleen into bilirubin. Levels of bilirubin above 2-3 mg/dl are visibly yellowish and may, in particular, adversely affect enzyme-based immunoassays. Such a condition is termed bilirubinaemia or icterus.
A sample containing lipemia may be whitish in color. Interferents may arise, for example, as a whitish appearance in serum or plasma portion due to the presence of excess lipids. Such a condition is called lipemia and lipid levels above about 50 mg/dl may interfere with antibody binding in immunoassays and may, accordingly, affect immunoassay results.
Thus, the degree of red color in a serum or plasma portion may correspond to the amount of hemolysis present, the degree of dark yellow/brown color may correspond to the amount of icterus present in the serum or plasma portion of the specimen, and the degree of whitish color may correspond to the amount of lipemia present in the serum or plasma portion of the specimen.
Subsequent to centrifugation, when the red blood cell portion has been separated from the serum or plasma portion, a skilled technician may visually inspect the serum or plasma portion and, if judged to not have a normal light yellow to light amber color, the specimen may be rejected. Otherwise, the specimen will be processed and analyzed as ordered. However, visual inspection is very subjective, labor intensive, and fraught with the possibility of human error. Thus, various methods have been implemented to ascertain whether hemolysis, icterus, and lipemia (these three conditions are frequently called “HIL”) are present in a serum or plasma portion of the specimen.
Typically, a laboratory technician will assign a hemolytic index, an icteric index, and a lipemic index to the serum and plasma portion based upon the color. Based upon the value of the hemolytic index, the icteric index, and the lipemic index, the interpretation of the results from the clinical analyzer can be evaluated. Alternately, if the value of one or more of the indexes is too high, the specimen may be rejected without analysis by the clinical analyzer. As mentioned above, visual inspection can be labor intensive and costly. Furthermore, the possibility of human error exists with visual inspection, the results of the visual inspection may be highly subjective and may vary between workers, and one variable could mask or hide other variables. Thus, it is becoming increasingly important to evaluate the integrity of the serum or plasma portion of the specimen without the use of visual inspection by a laboratory technician.
One attempt to solve this problem involves optically viewing the serum or plasma portion of the specimen after the specimen is transferred to one of the cuvettes of the clinical analyzer. Measuring the optical characteristics of the specimen in the clinical analyzer eliminates the need for visual inspection, but utilizes time on the clinical analyzer and, if the integrity of the specimen is determined to be compromised, additional machine time and a machine cycle is wasted. Furthermore, this procedure cannot be used with clinical analyzers that add reagents to the cuvette prior to adding the serum or plasma portion of the specimen.
One challenge in performing spectrophotometric analysis is that the specimens are initially obtained in a variety of types/sizes of primary patient sample collection containers (“sample containers”). These sample containers are usually tubes of varying diameters and lengths. In the case of a patient blood specimen, the liquid is often centrifuged to separate the serum or plasma portion from the cellular phase (e.g., red blood cell portion). Such sample containers may have a patient identification label, varying and unpredictable amounts of the serum or plasma portion, and can contain a varied amount of specimen liquid.
Because of the problems encountered when interferents are contained in specimens to be analyzed, there is an unmet need for methods and apparatus adapted to rapidly determine a presence of such interferents. The method and apparatus should not appreciably adversely affect the speed of obtaining analytical test results and should be deployable early in the processing so that corrective action by laboratory personnel minimizes delays in patient sample analysis. Furthermore, the method and apparatus should be able to be used on labeled sample containers.